Apparatus and method of bending pipe



July 8, 1969 J. w. RECKARD 3,453,857

I APPARATUS AND METHOD OI BENDNG PIPE Filed Oct. 21. 1966 sheet of 4 N Fig; l

' ATTORNEY.

July s, 1969 J. w. RECKARD` 3,453,857

APPARATUS ND METHOD OF BENDING PIPE Filed octal, 196e sheet o? of 4 INVENTOR.

JOHN W. RECKARD ATTORNEYS.

July v8, 1969 J. w. RECKARD 3,453,857

Y APPARATUS AND METHOD oF BENDING PIPE l Filed oct. 21. 1966 sheet 3 f 4 cmo@ L l 618 INVENTOR. JOHN W. RECKARD ATTORNEY.

July 8, 1969Y 1 w. RECKARD 3,453,857

APPARATUS AND METHOIIOF BENDING PIPE Filed Oct, 2l, 1966 Shee'fl 0f 4 VVlOZ 'IO4 v l04 24 INVENTOR. Y. JOHN w. RECKARD @#@QWW A ATTORNEYl United States Patent O U.S. Cl. 72-357 8 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for the cold bending of metallic pipe into an elbow tting wherein a force is applied upon the trailing end of a straight blank while the leading end is inserted in the tangential portion of a cavity which is bent to conform to the elbow fitting, interposing a mandrel in the other tangential portion of the cavity which has a removable end portion that extends around the bend of the cavity, and providing die halves forming the cavity which are mounted in a guide in such a manner that the radial forces developed internally in the pipe during the bending operation act to -keep the die halves closed and thus prevent formation of an undesirable longitudinal seam.

This invention relates to apparatus and method of bending metallic pipe and tubing.

It is well recognized in the art that in the forming of pipe fittings, such as elbows, changes occur in the pipe wall thickness, i.e. thinning occurs along the outer bend radius wall or heel and thickening at the inner bend radius wall. For this reason the A.S.T.M. has created a specification which states that the wall thickness at any point of the fitting must not be less than 87.5% of the nominal or standard thickness of the pipe.

It is the primary object of this invention to provide an apparatus and method of bending pipe under compression without the application of a positive restraining force on the leading end of the blank which will efiiciently produce a pipe fitting that meets the A.S.T.M. specification.

The bending of a pipe into an elbow with long tangents presents an additional problem, that is maintaining the integrity of the bend while a portion thereof straightens out to form one of the tangents. It is an important object of this invention to provide an apparatus and process for bending pipe under compression into an elbow with long tangents that maintains the integrity of the bend as well as the proper thickness at the heel thereof.

In the bending of pipe in -which a force is applied to the trailing end of the straight blank 'to push it into a die cavity, internal forces develop which push the pipe radially outwardly against the wall of the cavity, Often of magnitude suiicient to separate the die halves and thereby cause an undesirable longitudinal seam to be formed in the elbow. It is another object of this invention to provide an apparatus and method of bending pipe in which the die halves are provided with means whereby the aforesaid internal radial forces developed in the pipe as it is forced through the cavity tend to keep the die halves closed rather than open, thereby minimizing the possibility of producing the undesirable seam.

Another object of the invention is to provide an apparatus and method for bending pipe employing a lixed mandrel which is retained in a tangential portion of the die cavity so that the stock or work piece is forced around the mandrel, the mandrel being provided with a novel removable curved button which maintains the integrity of and prevents the collapse of the bend and at the same time 3,453,857 Patented July 8, 1969 ICC permits ready and easy removal of the mandrel from the bent pipe.

Another object of the invention is to provide an apparatus and method of bending pipe and particularly into elbows with tangential portions, which is relatively inexpensive and easy to operate.

These and other objects of the invention will become more apparent as the following description proceeds in conjunction with the accompanying drawings, wherein:

FIG. l is a vertical sectional view through the middle of the apparatus;

FIG. 2 is a perspective view of the straight blank or workpiece;

FIG. 3 is a perspective view of the bent elbow made from the workpiece and including tangential portions;

FIG. 4 isa group perspective View of the apparatus;

FIG. 5 is a sectional view taken on the line -5-5 of FIG .l and showing the die halves in the open position;

FIG. 6 is a view similar to FIG. 5 showing the die halves in the closed position;

FIG. 7 is a diagrammatic view, partly in section, illustrating the iirst stage in the bending process;

FIG. 8 is a view similar to FIG. 7 Showing an intermediate bending stage;

FIG. 9 is an enlarged elevational view of the inner end of the mandrel and illustrating the removable curved button;

FIG .10 is a sectional view taken on the line 1010 of FIG. 9; and

FIG. ll is a group elevational view of the button and the inner end of the mandrel.

Specific reference is now made to the drawings in which similar reference characters are used for corresponding elements throughout.

The present apparatus and method is designed to form a given length of a straight tubular blank or workpiece 10, made of stainless steel and similar metals, into an elbow 12 of radius 14, generally 90. There are many applications in the process industry requiring a pipe iitting in the form of an elbow having tangential portions 16, see FIG.

3, which extend as straight portions at substantially to each other beyond the curvature of the bend as is clearly shown in FIG. 3. These tangential portions are adapted to receive flanges which will not foul when the elbow is joined to other lengths of pipe. While the present invention is capable of bending the straight blank 10 into a short elbow, it is particularly well adapted to produce an elbow with tangential portions for a. purpose soon to appear.

Coming now to the apparatus itself, the same comprises a die box 18 having front and rear walls 20` and 22 and side walls 24 and 26 joining them. The member 18 is a xed member which is retained in a press frame 28 whose lower wall 30 contains an opening 32 through which a vertically disposed ram 34 extends which is operated by a conventional hydraulic or press cylinder 36 and which mounts a conventional platen 38. The bottom of the member 18 is either entirely opened to allow passage of the platen 38 or is an actual wall with an opening large enough to permit the vertical reciprocal movement therein of the platen 38 and the ram 34.

Similarly, the upper horizontal wall 40 of the press frame is provided with an opening 42 through which the ram 46 extends for vertical reciprocation, which ram is operated by a conventional press cylinder 48 and which also carries at its lower end a platen 50. The platen mounts a pilot 52, the upper portion 54 of which is of a diameter substantially equal to the outer diameter of the workpiece 10 and which includes a reduced portion 56 at its lower end which is adapted to enter into the workpiece 10` so that the shoulder 58 between the upper portion 54 and the lower portion 56 of the pilot will bear against the trailing end 60 of the workpiece.

The end walls 20 and 22 of the guide box 18 are each provided with vertically extending ribs 62 and 64, which are preferably rectangular in cross section, which project inwardly of the box 18 and which converge downwardly and inwardly thereof.

A pair of die holders 66 and 68 are provided, see FIG. 4, each with end walls 70` and 72 and channels 74 and 76 therein which also converge downwardly and inwardly and are of such shape and size as to slidably receive the guide ribs 62, 62 and 64, 64 of the opposite end walls 20 and 22 of the die holder guide box 18.

Each die box `66 and 68 contains an inner wall 78 which is provided with a substantially rectangular cut-out portion 80. Dies 82 and 84 are provided in the form of rectangular 'blocks which tit into the cut-out portions 80 of the die holders and there removably retained by suitable bolts 86. The inner faces 88 of the dies are provided with die cavities 90 of semi-circular cross section and of a shape to conform to that of the elbow to be made so that when the inner faces 88 of the dies meet, a cavity 92 is formed whose diameter approximates the outer diameter of the pipe or tubing and whose shape is that of the elbow desired, as shown in FIG. 3. The upper end of the semicircular die cavity 92, that is the end of the vertical tangential portion is provided with a semi-cylindrical enlarged opening 94 whereas a similar 4semi-cylindrical enlarged opening 96 is provided at the lower end of the semi-circular cavity or the end of the horizontal tangential portion. Thus, when the inner faces `88 of the dies 82 and 84 meet, not only is a die cavity 92 provided for the elbow with tangential portions to be formed, but enlarged cylindrical portions are also provided at the top and at the front side thereof.

The front wall 20 of the die box 18 is cut out as at 98 and includes a channel 100 peripherally around the cut-out portion to removably retain a gate member 102, which gate member may be manually positioned to close off the opening 98 or automatically positioned therein if it is carried by the upper platen `50. It will also be noted particularly from FIGS. l, and 6 that the die holders 66 and 68 rest upon the lower platen 38 so that when the platen 38 is raised by the press cylinder 36 to its uppermost position, the die holders are spread apart as shown in FIG. 5 and when the platen is lowered to its lowermost position, the inner faces `88 of the dies 82, 84 meet to provide the die cavity 92.

A mandrel 104 is provided which is an elongated rod whose diameter approximates the inner diameter of the pipe or tubing. One end of the mandrel is ground to provide a curved surface 106 which conforms to the radius of curvature of the heel of the bend desired in the elbow but which extends for only a portion of the overall length of the bend. Opposite to the curved portion 106 the mandrel is cut out as at 108 to provide axially extending recesses 110 forming between them a substantially ilat raised tongue or land portion 112.

Associated removably with this end of the mandrel is a button 114. Opening through one end of the button at its undersurface is a channel-shaped groove 116 which slidably receives the tongue or land 112 of the mandrel to provide a removable but snug t. It will be seen from FIGS. 9-11 that the mandrel and button are ground to provide certain surfaces which are essential in the bending process to retain the integrity of the bend of the elbow, i.e. prevent the collapse of the bend during formation thereof, and to permit formation of the front tangential portion 16 of the elbow without collapse of the pipe at the bend.

The formation of the surfaces will best be understood from a description of the manner in which the button 114 is made. A steel rod is yfirst bent to the required radius 14 of the finished pipe fitting or elbow 12. This rod is cut at the tangential points and 122 shown in dotted line in FIG. 3 and become the front and rear ends of the button. The groove 116 is then machined into the front end of the button for a snug removable iit on the end of the mandrel 104. Such a member when put into the end of the elbow fitting will not pass entirely therethrough. To effect this the heel is ground as at 124 and the lead end of the button is also contour ground so that in its nal form the button can be dropped through the fitting. The grinding olf of the heel and the contour grinding of the lead end of the member must be kept to a minimum to prevent the collapse of the bend of the elbow during its formation. Thus, it will be seen that the button 114 has a curved portion 126 at its lead end which conforms to the radius 125 of the inner curve of the desired elbow, an outer portion 128 on the opposite side thereof going to the trailing end of the button which conforms to a radius 130` of the outer curve or heel 118 of the bend of the elbow, a portion 124 which is ground out of the heel portion as well as additional contour grinding so that the Ibutton can be dropped through the fitting. The curved surfaces 106 and 128 together approximate the radius of the inner surface of the outer curve or heel 118 of the elbow even though the under grinding of the heel at 124 produces an interrupted or indented portion 132 when the button is assembled in place upon the end of the mandrel as shown in FIG. 9.

A die bushing 134 is provided to hold the workpiece 10 in the machine as well as a bushing 136 to hold the mandrel in place.

In use, press cylinder 36 is used to raise the platen 38 which raises and opens the die holders 66 and 68 and the dies 82 and 84 carried thereby. The mandrel 104 with the button 114 mounted on its end is slipped through the bushing 136 which is positioned and held in one of the semi-cylindrical openings at the forward end of the horizontally extending tangential portion of the die cavity 90. The bushing 134 is slipped over the workpiece 10 and placed in the semi-cylindrical opening 94 at the top of the vertically extending tangential portion of the die cavity 90 so that the leading end 138 of the workpiece embraces the trailing end 122 of the button 114, as shown in FIG. 7. The press cylinder 36 is then again actuated to lower the platen 38 whereupon the dies 82 and 84 are closed to form the cavity 92 whose inner wall is spaced from the outer surface of the mandrel 104 and its plug 114. The gate 102 is then dropped into the channel 100 so that it abuts the forward end 140 of the mandrel, as seen in FIGS. l, 7 and 8; Press cylinder 48 is then actuated whereupon the platen 50 is lowered and the pilot 52 enters the bushing 134 with the reduced portion 56 thereof entering the trailing end 60 of the workpiece 10 and the shoulder 58 bearing on the trailing end 60. The ram pressure thus forces the workpiece into the cavity 92. The initial stage is shown in FIG. 7. An intermediate stage is shown in FIG. 8 in which the bend in the pipe or tubing is rst formed. In FIG. l the complete bend is shown with the forward tangential portion straightening-out, so to speak. In this action the leading end 138 of the pipe pushes the mandrel support lbushing 136 forwardly toward the gate but the mandrel itself remains stationary.

As seen in FIG. 6, the press force 142 pushing the workpiece into and through the die cavity is in effect a compressive force -which is applied to the trailing end 60 of the workpiece and the bend in the workpiece with the straightening-out of the forw-ard tangential portion is effected without the application of a positive reactive force o-r restraint applied to the leading end of the workpiece. The reactive force on the workpiece or blank as it passes through the cavity is only the friction between the inner surface of the workpiece `and the outer surface of the mandrel and the removable button, and the friction between the outer surface of the workpiece and the inner surface of the die cavity. During the bending operation,

in which the mandrel and the button act to prevent the collapse of the bend, internal forces 144 are created in a direction radially outwardly of the pipe or tubing which normally tend to open the die halves with the result that the elbow is formed with an undesirable longitudinal seam. This is prevented in the instant invention because the radial forces 144 are resolved into vectors which act to keep the die halves 82 and 84 closed because they urge the die holders 66 and 68 downwardly into the closed position by virtue of the fact that they are mounted in the guide box 1S so as to converge when closed and to diverge when opened.

When the press is raised and the dies are opened, the bent pipe is removed with the mandrel from the machine and tapped free of the mandrel, at which time the plug separates from the mandrel and remains at the bent portion of the elbow from which it falls out freely of its own accord when the elbow is inverted.

While a preferred embodiment o-f the invention has here been shown and described, it will be understood that skilled artisans may make minor variations without departing from the spirit of the invention and the scope of the appended claims. Thus an hydr-aulic cylinder can be provided to automatically withdraw the mandrel from the bent pipe and the machine can be provided with electrical controls for periodically opening and closing the dies and raising and lowering the press which acts upon the workpiece to push it through the die cavity.

I claim:

1. Apparatus for cold bending metallic pipe or tubing into an elbow fitting comprising die halves `with semicavities therein adapted when mated to form an overall closed cavity having a bent portion and tangential extensions and conforming in shape and size to that of the elbow fitting desired, die holders mounting said dies so that said overall cavity extends in a generally vertical plane and one of said tangential extensions is horizontally disposed, means to move said die holders convergently together to form said overall cavity and divergently apart to open said overall cavity, and a mandrel including a body portion extending into said horizontally disposed tangential extension and an end portion removably mounted on said body portion and extending yaround said bend, the other tangential extension which is vertically disposed being adapted to receive a blank to be forced into said cavity around said mandrel.

2. The combination of claim 1 wherein said button is so shaped as to pass freely through the bent fitting but with close tolerance to the internal diameter of the fitting.

3. The combination of claim 2 wherein said button has a first surface portion with a radius substantially equal to that of the inner curve of the bend of the fitting, a second surface portion opposite to but longitudinally displaced from said first portion with a radius substantially equal to that of the outer curve of the bend of the fitting, saidy button having a third surface adjacent said second surface at the heel thereof which is ground down and contour surfaces elsewhere so that the button can pass freely through the bent fitting.

4. The combination of claim 1 wherein said means to move said die holders convergently together and divergently apart includes a fixed guide member, vertically extending downwardly converging interengaging ribs and channels coactive between said fixed guide member and said die holders, and means to raise and lower said die holders as a unit in said fixed guide member, said dies being mounted at the confronting faces of said die holders.

5. In an apparatus for cold bending metallic pipe or tubing into an elbow fitting, die halves with bent semicavities in generally vertical planes opening through the confronting faces thereof, die holders mounting said die halves, a fixed guide member, downwardly converging interengageable ribs and channels slidably mounting said die holders in said fixed guide member and means to raise and lower said die holders in said fixed guide member as a unit so that said semi-cavities close on the downstroke and open on the upstroke, the straight pipe or tubular blank being adapte-d to be forced through said closed cavities upon `application of a force downwardly on the blank.

6. In an apparatus for cold bending of metallic pipe or tubing into an elbow fitting including a die having a cavity formed of a bend and tangential portions conforming in shape and size to that of the elbow fitting desired, one tangential portion being a-dapted to receive a straight pipe or tubular blank upon which a force is to be applied to push it through the cavity, a mandrel including a body portion extending through the other tangential portion of the cavity and a button removably mounted on one end of said body portion and curving around the bend of said cavity, said button being so shaped as to be able to pass freely through the bent fitting, said blank being adapted to pass between the outer surface of said mandrel and button and the inner surface of said cavity.

7. The combination of claim 6 wherein said button has a first surface portion with a radius substantially equal to that of the inner curve of the bend of the fitting, a second surface portion opposite to but longitudinally displaced from said first portion with a radius substantially equal to that of the outer curve of the bend of the fitting, the said button having a third surface adjacent said second surface at the heel thereof which is ground down and contour surfaces elsewhere so that the button can pass freely through the bent fitting.

8. A method of cold bendingl metallic pipe or tubing into an elbow tting with tangential portions comprised of applying a force upon the trailing end of a straight blank of pipe or tubing while the leading end is inserted in the tangential portion of a cavity which is bent to conform in size and shape to the elbow fitting, and interposing a mandrel in the other tangential portion of said cavity having a removable end portion extending around the bend of the cavity, the applied force acting to move the blank through the cavity around the mandrel, the friction between the blank, mandrel and cavity being the sole restraining force to the movement of the blank through the cavity.

References Cited UNITED STATES PATENTS 2,358,857 9/1944 Gits 18-43 2,183,702 12/1939 Wendel 72-166 2,466,877 4/1949 Cross 72--3 69 X 2,701,002 2/1955 Arbogast 72-166 X 2,907,102 10/ 1959 Armstrong et al. 2,998,836 9/1961 Hitz 72--369 X 3,110,341 11/1963 Stalter 72-166 MILTON S. MEHR, Primary Examiner.;

U.S. Cl. X.R. 72-166, 359, 369 

